Transducers for underwater sound applications perform the functions of generating sound waves in the medium or detecting the existence of sound waves in the medium. Directional transducers are designed to project sound waves in a relatively narrow beam pattern and to receive sound waves generated by a source within the beam pattern while rejecting noise.
It is known to use piezoelectric ceramic tubes in fabricating various underwater acoustic transducer systems to provide rugged and relatively efficient transducers. For example, U.S. Pat. Nos. 2,733,423 and 4,823,041 disclose the use of piezoelectric ceramic tubes for both directional and omnidirectional applications, respectively. The 2,733,423 patent discloses the use a piezoelectric ceramic tube located in a case and insulated, on its bottom and sides, from the case by a sound insulating material. In this type of transducer, the directivity is produced by the insulating material, which damps the outer radial vibrations but does not interfere with the interior vibrations. The piezoelectric ceramic tube interior and the bore of the transducer are filled with a fluid having the same acoustic characteristic as water, which permits transmission of generated sounds in the forward direction only.
It is also known to use baffles in constructing efficient directional transducers. U.S. Pat. Nos. 4,004,266 and 3,922,572 disclose the use of steel or stainless steel plates as baffles. The heavy steel plate disclosed in the 4,004,266 patent, for example, prevents cross talk between closely spaced transducers in an array.
Piezoelectric ceramic tubes are also known for use in deep submergence transducers requiring operation at depths exceeding 10,000 feet. For example, U.S. Pat. No. 3,372,370 discloses a transducer which uses a pressure-accommodating mass of epoxy resin and microspheres to compensate for hydrodynamic loading and to absorb acoustic energy within the transducer. The microspheres make the resin incompressible and prevent high pressures from distorting the resin, which in turn would distort the transducer output.
Heretofore, a deep submergence, acoustically stable directional transducer has not been produced using acoustically tuned polyurethane or a waveguide adjacent to an air space.